Thermoplastic vulcaninates for run-flat tires

ABSTRACT

This invention relates generally to run-flat tires. More specifically, this invention relates to compounds comprising thermoplastic vulcanizates that are suitable for use in run-flat tire inserts.

FIELD

This invention relates generally to run-flat tires. More specifically,this invention relates to compounds comprising thermoplasticvulcanizates that are suitable for use in run-flat tire inserts.

BACKGROUND

The thermoplastic vulcanizate compositions of this invention can be usedin the production of a run-flat tire insert. Such run flat tires arevery well known in the art and are characterized by their ability to beused for some period of time in a deflated condition. In one design,this run-flat ability is created by the use of one or more fillers or“inserts” which stiffen the sidewalls and permit the tire to be drivenwhile uninflated as is described in U.S. Pat. Nos. 5,368,082, 6,263,935,and 5,871,600 (each fully incorporated herein by reference). In apreferred embodiment the thermoplastic vulcanizates of this inventionare used in the production of such “fillers” or “inserts” one or more ofwhich are in turn used as structural components in a pneumatic tire.These inserts may be disposed on the wheel inner rim between the tirebead flanges and extend radially outward from the wheel axis of rotationto support the tire in a deflated condition as described in U.S. Pat.No. 6,109,319. There are numerous methods of incorporating such insertsinto the tire including, but not limited to, those described in thepatents cited above as well as in U.S. Pat. Nos. 4,193,437, 4,405,007,5,639,320, 5,427,166, 5,868,190, 4,779,658, 4,917,164, 5,427,176,5,529,105, 5,494,958, 6,022,434, 5,238,040, 5,368,082, 5,427,166,5,511,599, 4,067,372, 4,287,924, 5,164,029, 5,217,549, 5,361,821,4,067,374, 5,309,970, 5,263,526, 5,439,041, 5,5385,800 5,526,862, and6,182,728 (describes “wedges” rather than inserts), U.S. Application No.2001/0001971 A1 and WO 01/42000 A1, EP 385,192, and EP 385,192 (eachfully incorporated herein by reference for their various descriptions of“insert,” “filler,” “wedge” design.) Despite decades of research,hundreds of publications, and millions of dollars devoted to this highlyvaluable technology, there still has yet to be developed an economicallyproduced run-flat tire that actually meets the needs of the generalpopulation.

The present invention describes new compositions which, whenincorporated into tire construction, provide improved run-flatcapability as well as recycleability in some embodiments. Thesecompositions comprise one or more thermoplastic vulcanizates.Thermoplastic vulcanizates are well known compounds that have been usedin a variety of applications but never before in run-flat tire inserts.

SUMMARY

This invention is directed to a run-flat tire comprising a thermoplasticvulcanizate. In an embodiment, the invention is directed to a run-flattire or insert comprising a thermoplastic vulcanizate having a propylenepolymer matrix phase and an ethylene based copolymer rubber phase. Inanother embodiment this invention is directed to a run-flat tire orinsert comprising a thermoplastic vulcanizate having a polyamide polymermatrix phase and ethylene based copolymer rubber phase. In anotherembodiment, the rubber phase further comprises a halogenated copolymerof isomonoolefin and alkylstyrene. In another embodiment, the rubberphase further comprises either a high crystallinity or low crystallinityethylene-propylene-diene terpolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows DSC traces of an embodiment of a thermoplastic vulcanizateof this invention, which illustrate that by substituting a lowcrystallinity ethylene-propylene-diene terpolymer for at least a portionof the rubber phase, the low temperature melting peak can be reduced.

DETAILED DESCRIPTION

A thermoplastic vulcanizate (TPV) is generally known to be areprocessable material that has at least one partially or fullycrosslinked rubbery component dispersed in a thermoplastic matrix. Athermoplastic vulcanizate possesses the properties of a thermosetelastomer and is reprocessable in an internal mixer. Upon reachingtemperatures above the softening point or melting point of the matrixphase a TPV can form continuous sheets and/or molded articles withcomplete knitting or fusion of the thermoplastic vulcanizate underconventional molding or shaping conditions for thermoplastics.

Generally, thermoplastic vulcanizates are prepared by blending thematerials for the matrix and rubber phases along with desired additivesand a cure package to promote at least partial crosslinking of therubber phase.

The most suitable thermoplastic vulcanizates for run-flat tires arethose that can withstand temperatures of at least 120° C. and providethe absorption necessary to reduce strikethrough and wear on thedeflated tire during operation.

Matrix Phase

The matrix phase portion of the thermoplastic vulcanizate may compriseany thermoplastic, including but not limited to polyolefins, polyamidessuch as nylon, or polyester. Suitable polymers for the matrix phase arethose thermoplastic polymers made by the polymerization of monoolefinmonomers using a high pressure, low pressure or intermediate pressureprocess with Ziegler Natta and/or metallocene catalysts. Preferably themonoolefin monomers converted to repeat units are at least 95 wt %monoolefins of the formula CH₂═C(CH₃)—R or CH₂═CHR where R is a H or alinear or branched alkyl group of from 1 to 12 carbon atoms.

Suitable polyolefins are polyethylene and polypropylene or theircopolymers and mixtures thereof. The polyethylene can be high density orlow density. The polypropylene can be a homopolymer or copolymer ormixtures thereof. Generally, the higher the melting temperature of theplastic phase the higher the potential use temperature of thethermoplastic vulcanizate.

Preferably, the matrix phase is based on a propylene polymer. Thispropylene polymer component can be any propylene-based polymer, i.e., apolymer wherein a majority of units are derived from propylene. Thuspropylene homopolymers, copolymers and impact copolymers may besuitable. A preferred propylene polymer is exemplified by ExxonMobilChemical's Escorene™ PP 1105 which is a homopolymer having a melt flowrate (MFR) of 35, a flexural modulus of 1300 MPa. Generally, thepropylene polymer should have a MFR of 15 or higher. The polypropylenepolymer can be made using single-site or multiple-site catalysts. Insome embodiments, metallocene or other single-site catalysts arepreferred.

The impact modified polypropylenes suitable for the matrix phase isitself a blend of a propylene polymer matrix with an uncrosslinkedelastomer rubber dispersed therein. Preferably the elastomer is acopolymer and the elastomer content is less than 20 wt % of the impactmodified polypropylene blend. The propylene polymer constituent of theimpact modified polypropylene is preferably a homopolymer of propylenehaving a propylene content of at least 95 wt % and a weight averagemolecular weight of at least 70,000. Preferably, the propylene polymeris highly stereoregular, either isotactic or syndiotactic regularity,with isotactic regularity being preferred.

The impact modified polypropylene may be prepared as a reactor blendwherein the isotactic propylene polymer and elastomer portion aresimultaneously formed by polymerization of propylene with anotherappropriate olefin comonomer in different zones or in a single reactionzone as is known in the art. Alternatively, the impact modifiedpolypropylene may be formed by melt compounding of a propylenehomopolymer with an elastomer, each of which were separately formedprior to blending. Generally, for reasons of economy, impact modifiedpolypropylenes are prepared as reactor blends and for this reasongenerally have an impact modifying elastomer content not exceeding about20 wt % of the reactor blend, and more typically not exceeding about 12wt % of the reactor blend. Further discussion of the particulars of animpact modified polypropylene may be found in U.S. Pat. No. 4,521,566.However the impact modified polypropylene is formed, it generallycomprises from about 80 wt % to about 90 wt % of a propylene polymer andfrom about 10 wt % to about 20 wt % of an elastomer such that thepropylene content of the blend is at least about 80 wt %. The impactmodified polypropylene has a 1% secant modulus of from about 60,000 psito about 130,000 psi, and a MFR of from about 0.5 to about 5.0 andpreferably from about 0.5 to about 3.

Thermoplastic polyamide compositions may also be used to form the matrixfor the thermoplastic vulcanizates of this invention. These generallycomprise crystalline or resinous, high molecular weight solid polymersincluding copolymers and terpolymers having recurring polyamide unitswithin the polymer chain. Polyamides may be prepared by polymerizationof one or more epsilon lactams such as caprolactam, pyrrolidone,lauryllactam and aminoundecanoic lactam, or amino acid, or bycondensation of dibasic acids and diamines. Both fiber forming andmolding grade nylons are suitable. Examples of such polyamides arepolycaprolactam (nylon 6), polylaurylactam (nylon 12),polyhexamethyleneadipamide (nylon 6,6), polyhexamethylene-azelamide(nylon 6,9), polyhexamethylenesebacamide (nylon 6,10),polyhexamethyleneisophthalamide (nylon 6,IP) and the condensationproduct of 11-aminoundecanoic acid (nylon 11); as well as partiallyaromatic polyamides made by polycondensation of meta xylene diamine andadipic acid. Furthermore, the polyamides may be reinforced, for example,by glass fibers or mineral fillers or mixtures thereof. Pigments, suchas carbon black or iron oxide may also be added. Additional examples ofpolyamides are described in Kirk-Othmer, Encyclopedia of ChemicalTechnology, v. 10, page 919, and Encyclopedia of Polymer Science andTechnology, Vol. 10, pages 392-414. Commercially available thermoplasticpolyamides may be advantageously used in the practice of this invention,especially those having a softening point or melting point between 160°C. to 275° C.

The matrix phase of the thermoplastic vulcanizate is from about 15 toabout 80 parts by weight, more preferably from about 25 to about 75parts by weight, and preferably from about 25 to about 50 parts byweight per 100 parts of the blend of thermoplastic plastic and therubber phase in the thermoplastic vulcanizate. The rubber is preferablyfrom about 20 to about 85 parts by weight, more preferably from about 25to about 75 parts by weight and preferably from about 50 to about 75parts by weight per 100 parts by weight of said blend in thethermoplastic vulcanizate. If the amount of plastic is based on theamount of rubber, it is preferably from about 15 to about 400 parts byweight, more preferably from about 30 to about 350 parts and preferablyfrom about 35 to about 300 parts by weight per 100 parts by weight ofthe rubber. Preferably, the final thermoplastic vulcanizates of thisinvention will, on a total olefin monomer content basis, contain fromabout 37 to about 51 weight % propylene units; from about 41 to about52.5 weight % ethylene units; from about zero to about 0.5 weight %diene units; and the balance will be from about 8 to about 10 weight %of units derived from a C₄ to C₈ alpha-olefin.

In a preferred embodiment, the proportion of impact modifiedpolypropylene resin component making up the matrix to the elastomercomponent making up the rubber phase provides the resultingthermoplastic vulcanizate composition with a 1% secant modulus of 50,000psi or less, preferably 40,000 psi or less, and most preferably 30,000psi or less.

Rubber Phase

The rubber phase can be based on any rubber having residual unsaturationor curable functional sites that can react and be at least partiallycrosslinked with curing agents. Suitable materials for the rubber thusinclude halobutyl rubber, EP and EPDM rubbers, natural rubber, syntheticrubbers such as synthetic polyisoprene, polybutadiene rubber,styrene-butadiene rubber, butadiene-acrylonitrile rubber etc. Aminefunctionalized or epoxy functionalized synthetic rubbers may be used.Examples of these include amine functionalized EPDM, and epoxyfunctionalized natural rubber and functionalized metallocene plastomer.These materials are commercially available.

In preferred embodiments, the rubber phase is based on an ethylenecopolymer, i.e., ethylene derived units are the major constituent byweight or mole %. Most preferred are those having a density of fromabout 0.915 g/cm³ to about 0.860 g/cm³ that are prepared with a singlesited catalyst, for example, a catalyst the transition metal componentsof which is an organometallic compound at least one ligand of which hasa cyclopentadienyl anion structure through which such ligand coordinatesto the transition metal cation. Such a catalyst system, now commonlyknown as “metallocene” catalyst, produces ethylene copolymers in whichthe comonomer is more randomly distributed within a molecular chain andalso more uniformly distributed across the different molecular weightfractions comprising the copolymer than has heretofore generally beenpossible to obtain with traditional types of heterogeneous multi-sitedZiegler-Natta catalysts. Metallocene catalysts are further described inU.S. Pat. Nos. 5,017,714 and 5,324,820.

These preferred ethylene copolymers are neither totallythermoplastic-like nor elastomer-like but are partially like athermoplastic and partially like an elastomer, sometimes referred to asa “plastomer”. Ethylene derived units will generally make up from about85 mole % to about 96 mole % of the these preferred ethylene copolymers;the alpha-olefin comonomer content comprises from about 15 to about 3.5mole % of the copolymer and is incorporated into the copolymer in anamount that provides for a density of from about 0.915 g/cm³ up to adensity of about 0.860 g/cm³. The distribution of the alpha-olefincomonomer within the preferred copolymers is substantially random andalso uniform among the differing molecular weight fractions thatcomprise the ethylene copolymer. This uniformity of comonomerdistribution within the copolymer, when expressed as a comonomerdistribution breadth index value (CDBI), provides for a CDBI greaterthan 60, preferably greater than 80, and more preferably greater than90. Further, these preferred ethylene copolymers are characterized by aDSC melting point curve that exhibits the occurrence of a single meltingpoint peak occurring in the region of 40° C. to 110° C. (second meltrundown), and the copolymer preferably has a weight average molecularvalue no less than 70,000 and no greater than 130,000, and the amolecular weight distribution (Mw/Mn) value of less than or equal to 4.0and preferably less than or equal to 3.5. Further, these preferredcopolymers have a 1% secant modulus not exceeding about 15,000 and aslow as about 800 psi or even less.

The EXACT™ elastomers are available from ExxonMobil Chemical. Theseplastomers are a copolymer of ethylene with a C₄-C₈ alpha-olefincomonomer and have a plastic-like molecular weight. This invention,however, can also be practiced using Engage™ polymers, a line ofmetallocene catalyzed plastomers available from Dow Chemical Company ofMidland, Mich.

The comonomer of the plastomer is preferably an acyclic monoolefin suchas butene-1, pentene-1, hexene-1, octene-1, or 4-methyl-pentene-1. Insome respects, it is desirable for the plastomer to be anethylene-alpha-olefin-diene terpolymer since incorporation of a quantityof diene monomer into the plastomer provides the plastomer with furtherresidual unsaturation to allow further functionalization and/orcross-linking reactions or coupling of the plastomers in the finishedrun-flat compound. In the case of a non-diene containing plastomer theresidual or chain end unsaturation, on the basis of the quantity ofterminal double bonds per 1,000 carbon atoms, would be of the vinyl type0.05 to 0.12, of the trans-vinylene type 0.06 to 0.15, and of thevinylene type 0.05 to 0.12.

Thus in a first preferred embodiment, this invention is directed to arun-flat tire insert comprising a thermoplastic vulcanizate having apropylene homopolymer or impact copolymer matrix phase and an ethylenebased copolymer rubber phase as described in detail above. In a secondpreferred embodiment, this invention is directed to a run-flat insertcomprising a thermoplastic vulcanizate having a polyamide polymer (e.g.,nylon) matrix phase, and an ethylene based copolymer rubber phase asdescribed in detail above.

In another embodiment, the TPV comprises a polypropylene homopolymer orimpact copolymer matrix phase and a rubber phase that comprises two ormore rubbers. Preferably the rubber phase of this embodiment comprises(A) an ethylene copolymer rubber phase having a C₄-8 alpha-olefincomonomer, having a plastic-like molecular weight, as described above(such as the EXACT™ elastomers), and (B) an ethylene-propylene-diene(EPDM) terpolymer.

The EPDM of component (B) above may be a low crystallinity EPDM or ahigh crystallinity EPDM. By low crystallinity EPDM, it is meant that theEPDM has a heat of fusion less than 10 Joules/gram (J/g), as determinedby DSC (first melt). A suitable low crystallinity EPDM terpolymer forthis embodiment of the invention is Vistalon™ 7500 (sold by ExxonMobilChemicals), which has an ethylene content of about 52.3 wt % and a heatof fusion of about 0.6 J/g. In some run-flat tire applications, theabsence of a low melting peak (as measured by DSC) is desirable, becausethe run-flat tire is designed to allow the flattened tire to travel atspeeds up to 50 miles/hour and at distances up to 90 miles. Theprolonged use of the flattened tire travelling at such speeds will causethe tire temperature to increase. It is believed that the presence of alow melting ingredient in the run-flat tire may compromise the tireperformance, such a handling, and cause excessive treadwear depending onthe specific design. The low melting peak (measured by DSC) can bereduced by substituting a portion of the plastomer rubber component witha low crystallinity EPDM. For example, referring now to FIG. 1, a TPVcomprising a polypropylene homopolymer matrix phase (Escorene™ PP 1105),and a rubber phase comprising an ethylene copolymer having a C₄-C₈alpha-olefin comonomer (Exact™ 8201, ethylene content 72.5 wt % and heatof fusion of 50 J/g) and a low crystallinity EPDM rubber (Vistalon™7500) has a reduced low temperature melting peak when compared to thesame TPV without the low crystallinity EPDM rubber. For the purposes ofthis embodiment of the invention, the low crystallinity EPDM componentcan comprise from about 50 wt % by weight to about 75 wt %, morepreferably about 60 wt % to about 70 wt % of the rubber phase. In thisregard, the ethylene copolymer of component (A) preferably has a densityless than 0.90 g/cm³, and more preferably a density between about 0.860g/cm³ and 0.880 g/cm³.

In another embodiment, the EPDM of component (B) is a high crystallinityEPDM. It is believed that the addition of a high crystallinity EPDM tothe rubber phase of this invention will improve the softness (flexuralmodulus and hardness) of the TPV. By high crystallinity EPDM, it ismeant that that the EPDM has an ethylene content of more than 70 wt %and a heat of fusion more that 10 J/g, as measured by DSC (first melt).Preferably the high crystallinity EPDM component comprises from about 20wt % to about 60 wt % of the rubber phase, more preferably about 25 wt %to about 50 wt % of the rubber phase. Preferred high crystalline EPrubbers are represented by ExxonMobil Chemical's Vistalon™ products.Most preferred is Vistalon™ 1703P which contains 0.9 wt % vinylnorbornene, and 78% ethylene content.

In another embodiment the rubber phase of the TPV further comprises ahalogenated copolymer of isomonoolefin and alkylstyrene as described inU.S. Pat. Nos. 5,162,445 and 6,207,754 (both fully incorporated hereinby reference). The thermoplastic vulcanizate compounds of this inventionmay also include various other components, for example, EP(D)M and EPrubber (EP) so that more processing oil can be added to reduce thestiffness of the final compound, as well as to improve processabilityand/or performance.

The halogenated copolymer which may be included in the rubber phase ispreferably a C₄ to C₇ isomonoolefin and an alkylstyrene. The halogenatedcopolymer can comprise from about 50 wt % by weight to about 75 wt %,more preferably about 60 wt % to about 70 wt % of the rubber phase.Suitable halogenated copolymers comprise between from about 0.5 to about50 weight percent, preferably from about 1 to about 20 weight percent,more preferably 2.0 to about 20 weight percent, of the alkylstyreneunits. The halogen content of the copolymer may range from above zero toabout 7.5 weight percent, preferably from about 0.1 to about 7.5 weightpercent.

The Mooney viscosity at 125° C. (ML 1+8) of such halogenated copolymersis typically between from about 20 to about 55, preferably from about 25to 45, most preferably from about 30 to about 35.

Such halogenated copolymers, as determined by gel permeationchromatography (GPC), have narrow molecular weight distributions andsubstantially homogeneous compositional distributions, or compositionaluniformity. Such copolymers include the alkylstyrene moiety representedby the formula:

in which each R is independently selected from the group consisting ofhydrogen, alkyl preferably having from 1 to 5 carbon atoms, primaryhaloalkyl having from 1 to 5 carbon atoms, secondary haloalkylpreferably having from 1 to 5 carbon atoms, and mixtures thereof and Xis selected from the group consisting of bromine, chlorine and mixturesthereof. The preparation of these polymers are well known as disclosedin U.S. Pat. No. 5,162,445 (fully incorporated herein by reference).Preferably, the isomonoolefin is isobutylene and the alkylstyrene ishalogenated methylstyrene wherein the halogen is bromine. Thepara-isomer is particularly preferred.

The halogenated copolymer for use in this invention may be produced byhalogenating an isobutylene-alkylstyrene copolymer using bromine innormal alkane (e.g., hexane or heptane) solution utilizing a bis azoinitiator, e.g., AIBN or VAZO 52 (2,21-azobis(2,4 dimethylpentanenitrile)), at about 55° C. to 80° C. for a time period ranging fromabout 4.5 to about 30 minutes, followed by a caustic quench. Therecovered polymer is then washed in basic water wash andwater/isopropanol washes, recovered, stabilized and dried. At leastabout 95 weight percent of the resulting halogenated copolymer for usein this invention has a halogenated alkylstyrene content within about 10weight percent, and preferably within about 7 weight percent, of theaverage alkylstyrene content for the overall composition, and preferablyat least 97 weight percent of the copolymer product has an alkylstyrenecontent within about 10 weight percent and preferably about 7 weightpercent, of the average alkylstyrene content for the overallcomposition.

The thermoplastic vulcanizates of this invention may be formed fromother components or additives, such as processing oil and moisturegenerating agent, Epsom salt, primary, secondary antioxidants, andprocessing aids.

Curing

Curing can be effected by any of the well known curing systems,including sulfur and sulfur donor cure systems, peroxide cure, andquinone type cure systems, and silane coupling agents. There are severalmethods of crosslinking the rubber phase using chemical agents. Onecommon method involves the use of peroxide, such as dicmyl peroxide, toform carbon to carbon bonds. However, this method is not useful when thematrix phase is based on propylene polymer because the peroxide willsimultaneously degrade the polypropylene. Another issue with peroxidecrosslinking is the tendency to scorch (premature crosslinking) duringprocessing. An alternate method involves the use of vinylalkoxysilanes,such as vinyltrimethoxy silane (VTMOS) or vinyltrimethoxysilane (VTEOS)in conjunction with a very small peroxide, i.e., a ratio ofvinylalkoxysilane/peroxide of from 10/1 to 40/1. VTMOS is preferredbecause the grafted rubber can be crosslinked rapidly during reactivecompounding. By careful selection of low firing peroxide, degradation ofpolypropylene can be avoided. The peroxide will trigger the graftingreaction of VTMOS onto the plastomer and the grafted VTMOS cansubsequently crosslink promoted by a hydrolysis catalyst such asdibutyltin dilaurate, in the presence of moisture.

In a preferred embodiment, the thermoplastic vulcanizate is formed bycrosslinking via a specifically formulated silane masterbatch, whichcontains a built-in moisture generating compounding step. Such a processis disclosed in U.S. Pat. No. 5,112,919, incorporated herein byreference, which provides a process for adding a solid feed of silanecrosslinking agent into an extruder, as opposed to liquid silane. Theinjection of liquid silane typically requires an expansive meteringdevice to ensure an accurate dosage control. Inaccurate dosage controlcan lead to coating of the extruder screw with silane, which willtypically lead to fouling and equipment shut down. The moisturegenerating agent releases hydrated water upon heating inside thecompounding equipment, which enables the crosslinking to occur.Non-limiting examples include adding inorganic salt and clay. Combininga metal oxide and a carboxylic acid during the melt compounding can alsobe performed to release water into the melt. In some cases, directinjection of a small amount of water into a twin screw extruder can beperformed.

Two types of silane masterbatch are commercially available. One type isbased on a porous polyethylene carrier, and the other type is based on aporous polypropylene carrier. For thermoplastic vulcanizates having apropylene-based matrix, the preferred carrier is porous polypropylene.More preferably, the polypropylene carrier is a polypropylenehomopolymer or a polypropylene impact copolymer. Polypropylene randomcopolymers are not preferred because the vinylsilane will graft onto theethylene linkages along the backbone of the polypropylene randomcopolymer and crosslink both the carrier resin as well as the dispersedrubber particles.

In another embodiment, engineering resins such as polyamide orthermoplastic polyesters are used as carrier resins in order to increasethe high temperature resistance of the TPV. Maleic anhydride graftedplastomers or maleic, anhydride grafted EP rubber or EPDM can be used asa compatibilizer between the engineering resin and the rubber phase.Peroxide and vinylsilane can also be used. Therefore, during reactivecompounding of nylon TPV or polyester TPV, either a silane masterbatchor a peroxide masterbatch can be used to crosslink the rubber phase.

Run-Flat Tire Insert

A particularly preferred run-flat tire insert construction is based on athree-layer design wherein each layer comprises a thermoplasticvulcanizate of this invention. The outer layer in this embodimentincludes ultra high molecular weight polyethylene powders (UHMWPE) witha specific gravity at 23° C. of 0.925 to 0.940 or ground tire treadswhich confers abrasion resistance. The innermost layer includes a talcadditive that provides stiffness, stability and a snug fit on the innerwheel rim. Other mineral fillers or chopped fiberglass can also be usedfor this purpose.

The middle layer is a foamed thermoplastic vulcanizate. This foam may beprepared by any number of well known techniques, for example, thosedescribed in U.S. Pat. No. 5,939,464. Generally, thermoplasticelastomers have been foamed using chemical blowing agents, low-boilinghydrocarbons, or chlorofluorocarbons as foaming agents. These havedrawbacks, based on environmental considerations. Although thechlorofluorocarbons have been widely and effectively used in foamingthermoplastic elastomers, their perceived threat to the ozone layer hasprompted a search for alternative foaming methods which do not possessenvironmental hazards or present any of the other drawbacks. Otherfoaming agents include isobutane, azodicarbonamides, sodium bicarbonate,sodium carbonate, etc. The process for using chemical blowing agents isexplained in trade literature from companies such as Ready InternationalCorp. in Keyport, N.J.

It has been found that thermoplastic vulcanizates can be foamed byheating them to above their melting point, admixing with a minor amountof water under pressure, and then releasing the mixture to atmosphericpressure. Excellent foaming can be accomplished with water as the solefoaming agent.

Regardless of how the thermoplastic vulcanizates of this invention areincorporated into the tire structure, run-flat capability is directlydependent on the use of such thermoplastic vulcanizates. Preferablythese run-flat tire inserts are capable of providing at least 90 milesof use at 50 MPH without significant tire damage and with safe handling,that is the run-flat tires are capable of withstanding temperatures ofat least 120° C. and providing the absorption necessary to reducestrikethrough.

EXAMPLES

The present invention is illustrated hereinafter in more detail withreference to the following examples, which should not be construed as tolimit the scope of the present invention. Table 1 provides a list of thetest methods used in the examples.

In the following examples, Escorene™ PP 1105 is a propylene homopolymerhaving a melt flow rate of 35, a flexural modulus (MPa) of 1300, and aNotched Izod Impact (@23° C. KJ/m²) of 3.2. Escorene™ PP 8191 is animpact modified polypropylene having a density of 0.9 g/cm³, a melt flowrate of 1 dg/min, an ethylene comonomer content of 20 wt %, a 1% secantmodulus of 62,500 psi and a DSC peak melting point of 141.6° C. Capron™CA 73 ZP is a polyamide-6 resin from Honeywell, Morristown, N.J. Ultamid35 is a polyamide 6,66 copolymer from BASF, Freeport, Tex. Pebax 3533 isa flexible polyamide from Atofina Chemical, Philadelphia, Pa. Sunpar 150HT is a processing oil from Sun Oil, Marcus Hook, Pa. Exact™ 8201 is anethylene-octene copolymer having a melt index of 1.1 g/10 min, a densityof 0.882 g/cm³, a flexural modulus 1% secant of 3300 psi, a Mooneyviscosity (1+4 @125° C.) of 19, a peak melting temperature of 66.7° C.,and a melt flow rate of 2.5 g/10 min. Exact™4033 is an ethylene-butenecopolymer having a density of 0.880 g/cm³, a melt index of 0.8 dg/10min., a flexural modulus 1% secant of 3300 psi, a Mooney viscosity (1+4@125° C.) of 28 and a DSC peak melting point of 60° C. Vistalon™ 1703Pis a high crystallinity EPDM containing about 0.9 wt % vinyl norborneneand 78 wt % ethylene. Vistalon™ 3666 is an oil extended low crystallineEPDM with 0 J/g heat of fusion. Vistalon™ 9303H is another lowcrystalline EPDM having a 3.7 J/g heat of fusion. Exxpro™ 89-1 is abrominated polymer derived from a copolymer of isobutylene andmethylstyrene. Exxpro™ 89-1 has a density of 0.93 g/cm³, a Mooneyviscosity of 35 ML (1+8) @ 125° C. and a bromine wt % of 1.2.

Escorene™, Exact™, Vistalon™ and Exxpro™ are products available fromExxonMobil Chemical Company. The Silane masterbatch used was supplied byOSi Specialties, Crompton Corporation, Tarrytwon, N.J., under thedesignation of XL-Pearl Y-15307, which comprises a 70 wt % silanecocktail absorbed into 30 wt % porous polypropylene. The majority of thesilane cocktail comprises a VTMOS type of silane with grafting peroxideand hydrolysis catalyst added. A commercial supplier of porous carrieris supplied by Accurel Systems, Akzo Nobel Membrana Gmbh, Obernburg,Germany. TABLE 1 Test Method Melt Flow Rate ASTM D1238 Shore HardnessASTM D2240 Conditioning of Test Specimens ASTM D618 Tensile StrengthASTM D638 Tensile Modulus ASTM D638 Ultimate Elongation ASTM D638Flexural Modulus ASTM D790 DSC Peak Melting Point ASTM D3417 Gel ContentASTM D- 2765 Compression Set ASTM D-395

Example 1

In Samples 1 through 5, various amounts of silane masterbatch (from 1.5parts per hundred to 3.5 parts per hundred resin) were added to 30/0blends of Escorene™ PP 1105/Exact™ 8201 and the mixture melt mixed in a0° C. size Banbury mixer to perform a silane grafting reaction. A batchweight of 2270 grams was used. After the silane grafting reaction wascompleted, as indicated by a motor torque increase, the feed ram wasraised, and 0.2 parts of Epsom salt per hundred parts of resin wasadded. The ram was then lowered until another torque increase wasobserved. In order to prevent the material from being heated up to above500 F, the mixer was shifted to a lower rotor speed to complete thecrosslinking reaction. As shown in Table 2, an increased amount ofsilane masterbatch results in increased gel content, reduced compressionset, reduced elongation at break, and a slight decrease in tensilestress and flexural modulus. TABLE 2 Sample Sample Sample Sample Sample1 2 3 4 5 Composition Escorene ™ PP 1105 30 30 30 30 30 EXACT ™ 8201 7070 70 70 70 Silane Masterbatch 1.5 2 2.5 3 3.5 Epsom Salt 0.2 0.2 0.20.2 0.2 Property Hardness, Shore D @ 0 sec Elapsed 47 47 49 49 48 Time @15 sec Elapsed 43 43 44 44 42 Time Tensile Stress, psi 100% Modulus 13371272 1267 1165 1187 200% Modulus 1464 1421 1445 1324 1375 300% Modulus1556 1548 1598 1472 1549 Ultimate 2497 2297 2207 2322 2293 UltimateElongation, % 1167 832 665 742 663 Flexural Modulus, psi Tangent 1980419163 16369 15791 15257 1% Secant 19308 18561 15994 15360 14840 TearStrength, lbs/in @ Max Load 484.4 418 364.8 341.7 348.8 @ Break 241249.5 214.6 173.6 248.9 Compression Set, % @ 70 C. & 22 hrs 83 77 74 7072 Xylene Extractables, % 31.97 46.24 50.3 59.77 59.82

Example 2

Samples 6-11 of Table 3 illustrate thermoplastic vulcanizates having apropylene homopolymer matrix phase and an ethylene based copolymerrubber phase produced by a continuous mixer, as described in detailbelow. The same resin mixture of Escorene™ PP 1105/Exact™ 8201 asdescribed in Example 1, together with the silane masterbatch is firstmelt compounded using a 30 mm ZSK twin screw extruder to complete thesilane grafting reaction. In a second pass, the melt blended compoundtogether with Epsom salt was compounded on the same ZSK extruder tocomplete the crosslinking reaction. The same trends of silane additionon properties are observed as in Table 2. TABLE 3 Sample Sample SampleSample Sample Sample 6 7 8 9 10 11 Composition Escorene ™ PP 30 30 30 3030 30 1105 Exact ™ 8201 70 70 70 70 70 70 Silane 2 2.5 3 3.5 4 4.5Masterbatch Epsom Salt 0.2 0.2 0.2 0.2 0.2 0.2 Property Hardness, ShoreD @ 0 sec 47 46 46 45 47 46 Elapsed Time @ 15 sec 42 41 42 40 42 40Elapsed Time Tensile Stress, psi 100% Modulus 1267 1180 1221 1190 12241248 200% Modulus 1387 1325 1395 1460 1497 1545 300% Modulus 1477 14481542 1698 1674 1751 Ultimate 2500 2400 2462 1766 1870 1893 Ultimate 1142923 879 345 369 346 Elongation, % Flexural Modulus, psi Tangent 1846617703 16547 15701 15725 15383 1% Secant 18442 17501 16523 15310 1548215222 Tear Strength, lbs/in @ Max Load 444 397 392 356 349 342 @ Break265 216 218 217 224 202 Compression Set, % @ 70 C. & 80 78 72 76 66 6622 hrs Vicat Softening Point @ 1000 g 74.9 75.3 75.8 86.4 86.8 97.1Xylene 39.12 52.62 54.24 63.83 64.56 65.4 Extractables, %

Example 3

Samples 12-17 of Table 4 illustrate TPV compositions having a propylenehomopolymer matrix phase, and a rubber phase comprising a combination ofa metallocene plastomer and a low crystallinity EPDM rubber. Each ofthese compositions shows only a polypropylene melting peak by DSC, andno secondary low temperature peak was observed. Also in Sample 14 theBurgess clay served as both a moisture generation agent and areinforcing agent as indicated by the higher tensile strength of thenon-clay containing compounds. TABLE 4 Composition Sample 12 Sample 13Sample 14 Sample 15 Sample 16 Sample 17 Escorene ™ PP 30 30 30 30 30 301105 Exact ™ 8201 23 23 23 Vistalon ™ 3666 47 70 Vistalon ™ 7500 47 70Vistalon ™ 47 70 9303H Silane 3.4 3.4 3.4 3.4 3.4 3.4 Masterbatch Sunpar150 HT 10 10 10 10 Epsom Salt 0.2 0.2 0.2 0.2 0.2 0.2 Burgess Clay 2103.5 Property Hardness, Shore 79 78 78 71 78 74 A @15 sec. UltimateTensile, 857 579 1065 486 831 602 psi Elongation at 316 321 745 206 622410 Break

Example 4

Samples 18-20 of Table 5 illustrate TPV compositions having a propylenehomopolymer matrix phase, and a rubber phase comprising a combination ofmetallocene plastomer and a high crystallinity EPDM rubber. As shown inTable 5, the substitution of a high crystallinity EPDM such as Vistalon1703P (78 wt % ethylene and 36.5 J/g heat of fusion) for EXACT™ 8201 inthis embodiment improves the softness (flexural modulus and hardness) ofthe TPV. Based on the gel content results, it is apparent thatvinylsaline can be simultaneously grafted to both EXACT™ 8201 andVistalon™ 1703P and crosslinked by the same type and amount of moisturegenerating agent, (Epsom salt). TABLE 5 Sample 18 Sample 19 Sample 20Composition Escorene ™ PP 1105 29.1 29.1 29.1 Exact ™ 8201 68 48 38Vistalon ™ 1703P 20 30 Silane Masterbatch 2.9 2.9 2.9 Epsom Salt 0.2 0.20.2 Sunpar 150HT 5 5 5 Property Melt Flow Rate @ 10X, dg/min 2.9 4.2 8Shore D Hardness 48.4 45.2 42.2 Ultimate Tensile Stress, psi 1980 17851527 Elongation @ Break, % 434 448 410 Tensile Modulus, psi  15% 330 367268 100% 1263 1125 1005 200% 1528 1354 1220 300% 1741 1542 1388 FlexuralModulus-1% Secant, 16855 14606 12584 psi Tear Resistance, lbf/in @ MaxLoad 359 363 319 @ Break 213 211 183 Compression Set, RT & 22 hr, 42.444 45.1 % Xylene Insolubles, % 58.65 53.51 47.57

All compositions shown in Table 5 were produced by two pass compoundingusing a 30 mm ZSK twin screw extruder. All ingredients were firstblended together and fed into the extruder to complete the silanegrafting reaction. In a second pass extrusion, Epsom salt was compoundedtogether with the materials produced from the first pass to complete thecrosslinking reaction. Samples 19 and 20 show a decrease in stiffness(flexural modulus), as compared to comparative sample 18, as moreVistalon™ 17003 P is used to replace the stiffer Exact™ 8201.

Example 5

TPV compositions were prepared with an impact modified polypropylenecopolymer (Escorene™ PP 8191) as the matrix phase, and a rubber phasecomprising a metallocene plastomer (Exact™ 4033) and a halogenatedrubber (Exxpro™ 89-1), as shown in Table 6. TABLE 6 Sample 21 Sample 22Sample 23 Composition Escorene ™ PP 8191 40 40 40 Exact ™ 4033 55 5547.5 Exxpro ™ 89-1 5 5 12.5 Zinc Oxide 0.05 0.2 Zinc Stearate 0.05 0.2Property Melt Flow Rate @ wt, dg/min 1 0.9 0.1 Flexural Modulus, 1%secant, psi 23900 22000 20500

In the presence of zinc oxide and zinc stearate, the plastomer can begrafted onto the halogenated rubber. But the combination of zincoxide/zinc stearate is ineffective in crosslinking the plastomer,itself. The extra amount of zinc oxide and zinc stearate present can beused to crosslink the halogenated rubber. Sample 21 shows that bysubstituting 5 parts of the halogenated rubber for the plastomer, theresulting blend has a melt flow rate of 1 dg/min. Sample 22 is identicalto Sample 21, except that 0.05 parts of zinc oxide per hundred parts ofresin and 0.05 parts of zinc stearate per hundred parts resin wereadded. The resultant composition showed a slight decrease of melt flowrate due to crosslinking of the 5 parts of halogenated rubber. In Sample23, 12.5 parts of the halogenated rubber was used to replace an equalamount of the plastomer, and the melt flow rate decreased to 0.1 dg/min,indicating an increased degree of crosslinking in the compound.

While the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. Also, different types of members and configurations of memberscan be formed in accordance with the invention, in a number of differentways that will be apparent to persons having ordinary skill in the art.Therefore, the spirit and scope of the appended claims should not belimited to the description of the preferred versions contained herein.

All documents cited herein are fully incorporated by reference for alljurisdictions in which such incorporation is permitted and to the extentthey are not inconsistent with this specification. All documents towhich priority is claimed are fully incorporated by reference for alljurisdictions in which such incorporation is permitted. Althoughdependent claims have single dependencies in accordance with U.S.practice, each of the features in any of the dependent claims can becombined with each of the features of one or more of the other dependentclaims dependent upon the same independent claim or claims.

1) A run-flat tire insert comprising a thermoplastic vulcanizate. 2) Therun-flat tire insert of claim 1, wherein said thermoplastic vulcanizatecomprises a thermoplastic matrix phase and an at least partiallycross-linked rubber phase. 3) The run-flat tire insert of claim 2,wherein the matrix phase comprises about 15 to about 80 parts by weightand the rubber phase comprises about 20 to 85 parts by weight per 100parts by weight of the thermoplastic vulcanizate. 4) The run-flat tireinsert of claim 2, wherein said thermoplastic matrix phase comprises atleast one of a polyolefin, a polyamide and a polyester. 5) The run-flattire insert of claim 4, wherein said polyolefin comprises at least oneof a polyethylene, a polypropylene, a polyethylene copolymer, and apolypropylene copolymer. 6) The run-flat tire insert of claim 2, whereinthe thermoplastic matrix phase comprises a blend of a polypropylenecomponent and an uncrosslinked elastomeric rubber component. 7) Therun-flat tire insert of claim 6, wherein said uncrosslinked elastomericrubber component comprises less than 20 wt % of said blend. 8) Therun-flat tire insert of claim 6, wherein said polypropylene component isa polypropylene homopolymer having a molecular weight of at least70,000. 9) The run-flat tire insert of claim 4, wherein said polyamidehas a melting point of between 160° C. and 275° C. 10) The run-flat tireinsert of claim 4, wherein said polyamide comprises nylon. 11) Therun-flat tire insert of claim 10, wherein said nylon is selected from atleast one of polycaprolactam (nylon 6), polylaurylactam (nylon 12),polyhexamethyleneadipamide (nylon 6,6), polyhexamethylene-azelamide(nylon 6,9), polyhexamethylenesebacamide (nylon 6,10),polyhexamethyleneisophthalamide (nylon 6,IP) the condensation product of11-aminoundecanoic acid (nylon 11) and partially aromatic polyamidesmade by polycondensation of meta xylene diamine and adipic acid. 12) Therun-flat tire insert of claim 2, wherein the at least partiallycross-linked rubber phase comprises at least one of halobutyl rubber,ethylene-propylene rubber, ethylene-propylene-diene terpolymer rubber,natural rubber, synthetic rubber, amine functionalized synthetic rubber,and epoxy functionalized synthetic rubber. 13) The run-flat tire insertof claim 2, wherein the at least partially cross-linked rubber phasecomprises an ethylene copolymer, having about 85 mol % to about 96 mol %ethylene units, about 4 mol % to about 15 mol % alpha-olefin units, adensity from about 0.915 g/cm³ to about 0.860 g/cm³, and a CDBI ofgreater than
 60. 14) The run-flat tire insert of claim 13, wherein saidethylene copolymer is characterized by a single melting point peak inthe region of 50° C. to 110° C. as measured by DSC (second meltrundown). 15) The run-flat tire insert of claim 13, wherein saidethylene copolymer has a weight average molecular value of between70,000 and 130,000. 16) The run-flat tire insert of claim 13, whereinsaid ethylene copolymer has a 1% secant modulus less than 15,000. 17)The run-flat tire insert of claim 2, wherein the at least partiallycross-linked rubber phase comprises an ethylene copolymer and anethylene-propylene-diene terpolymer, said ethylene copolymer havingabout 85 mol % to about 96 mol % ethylene units and about 4 mol % toabout 15 mol % alpha-olefin units. 18) The run-flat tire insert of claim17, wherein said at least partially cross-linked rubber phase comprisesfrom about 25 wt % to about 50 wt % of said ethylene copolymer and about50 wt % to about 75 wt % of a low crystallinity ethylene-propylene-dieneterpolymer. 19) The run-flat tire insert of claim 17, wherein said atleast partially cross-linked rubber phase comprises from about 40 wt %to about 80 wt/o of said ethylene copolymer and about 20 wt % to about60 wt % of a high crystallinity ethylene-propylene-diene terpolymer. 20)The run-flat tire insert of claim 2, wherein the at least partiallycross-linked rubber phase comprises (a) about 25 Wt/o to about 50 wt %of an ethylene copolymer having about 85 mol % to about 96 mol %ethylene units and about 4 mol % to about 15 mol % alpha-olefin units,and (b) about 50 wt % to about 75 wt % of a halogenated copolymer of aC₄ to C₇ isomonoolefin and an alkylstyrene. 21) The run-flat tire insertof claim 20, wherein said halogenated copolymer comprises about 0.5 wt %to about 50 wt % alkylstyrene units. 22) The run-flat tire insert ofclaim 20, wherein said halogenated copolymer comprises halogen units offrom about 0.1 wt % to about 7.5 wt %. 23) The run-flat tire insert ofclaim 20, wherein said halogenated copolymer has a Mooney viscosity at125° C. (ML 1+8) of from about 20 to about
 55. 24) The run-flat tireinsert of claim 20, wherein said isomonoolefin comprises isobutene. 25)The run-flat tire insert of claim 20, wherein said alkylstyrenecomprises halogenated methylstyrene. 26) The run-flat tire insert ofclaim 20, wherein said halogen is bromine. 27) A run-flat tire insertcomprising a thermoplastic vulcanizate having a propylene polymer matrixphase and ethylene based copolymer rubber phase. 28) The run-flat tireinsert of claim 27, wherein said polypropylene polymer matrix phasecomprises a polypropylene homopolymer having a molecular weight of atleast 70,000. 29) The run-flat tire insert of claim 27, wherein saidpolypropylene polymer matrix phase comprises an impact copolymer. 30)The run-flat tire insert of claim 27, wherein the propylene polymermatrix phase comprises about 15 to about 80 parts by weight and theethylene based copolymer rubber phase comprises about 20 to 85 parts byweight per 100 parts by weight of the thermoplastic vulcanizate. 31) Therun-flat tire insert of claim 27, wherein the ethylene based copolymerrubber phase comprises an at least partially crosslinked copolymerhaving about 85 mol % to about 96 mol % ethylene units, about 4 mol % toabout 15 mol % alpha-olefin units, a density from about 0.915 g/cm³ toabout 0.860 g/cm³, and a CDBI of greater than
 60. 32) A run-flat tireinsert comprising a thermoplastic vulcanizate having a polyamide matrixphase and ethylene based copolymer rubber phase. 33) The run-flat tireinsert of claim 32, wherein said polyamide has a melting point ofbetween 160° C. and 275° C. 34) The run-flat tire insert of claim 32,wherein said polyamide comprises nylon. 35) The run-flat tire insert ofclaim 34, wherein said nylon is selected from at least one ofpolycaprolactam (nylon 6), polylaurylactam (nylon 12),polyhexamethyleneadipamide (nylon 6,6), polyhexamethylene-azelamide(nylon 6,9), polyhexamethylenesebacamide (nylon 6,10),polyhexamethyleneisophthalamide (nylon 6,IP) the condensation product of11-aminoundecanoic acid (nylon 11) and partially aromatic polyamidesmade by polycondensation of meta xylene diamine and adipic acid. 36) Therun-flat tire insert of claim 32, wherein the ethylene based copolymerrubber phase comprises an at least partially crosslinked copolymerhaving about 85 mol % to about 96 mol % ethylene units, about 4 mol % toabout 15 mol % alpha-olefin units, a density from about 0.915 g/cm³ toabout 0.860 g/cm³, and a CDBI of greater than
 60. 37) A run-flat tireinsert comprising a thermoplastic vulcanizate having a polypropylenehomopolymer matrix phase and an at least partially crosslinked rubberphase comprising an ethylene copolymer having about 85 mol % to about 96mol % ethylene units, about 4 mol % to about 15 mol % alpha-olefinunits, a density from about 0.915 g/cm³ to about 0.860 g/cm³, and a CDBIof greater than
 60. 38) The run-flat tire insert of claim 37, whereinsaid alpha-olefin units comprise octene units. 39) The run-flat tireinsert of claim 37, wherein said alpha-olefin units comprise buteneunits 40) The run-flat tire insert of claim 37, wherein saidalpha-olefin units comprise hexene units. 41) A run-flat tire insertcomprising a thermoplastic vulcanizate having a polypropylenehomopolymer matrix phase and a rubber phase comprising (a) an at leastpartially crosslinked ethylene copolymer having about 85 mol % to about96 mol % ethylene units, about 4 mol % to about 15 mol % alpha-olefinunits, a density from about 0.915 g/cm³ to about 0.860 g/cm³, and a CDBIof greater than 60, and (b) an ethylene-propylene-diene terpolymer. 42)The run-flat tire insert of claim 41, wherein saidethylene-propylene-diene terpolymer has a heat of fusion less than 10J/g. 43) The run-flat tire insert of claim 41, wherein saidethylene-propylene-diene terpolymer has an ethylene content of greaterthan 70 wt % and a heat of fusion more than 10 J/g. 44) A thermoplasticvulcanizate comprising a polypropylene homopolymer matrix phase and arubber phase comprising (a) about 25 wt % to about 50 wt % of an atleast partially crosslinked ethylene copolymer having about 85 mol % toabout 96 mol % ethylene units, about 4 mol % to about 15 mol %alpha-olefin units, a density from about 0.915 g/cm³ to about 0.860g/cm³, and a CDBI of greater than 60, and (b) about 50 wt % to about 75wt % of a low crystallinity ethylene-propylene-diene terpolymer having aheat of fusion less than 10 J/g.